In recent years, studies have been actively made on magnetic field sensor devices being made highly sensitive, developments of magnetic memory devices, etc., utilizing a so-called magneto-resistance effect that is the effect of varying resistance with a change in external magnetic field. The competition among researchers and developers for these devices falling in one of the advanced technical fields that support the information technology developing at ever-progressing speed is being intensified.
The magneto-resistance materials have been developed using various kinds of materials having various structures. Magnetic metal alloys, such as Permalloy, have heretofore been used as materials for magnetic field sensors and magnetic heads. However, the magneto-resistance effect thereof has been at several % at most, and other materials have already been substituted in the present state of affairs.
As one of relatively new magneto-resistance materials, there can be cited a multi-layer structure alternating a magnetic substance and a non-magnetic substance. Attention has been paid to this multi-layer structure because it exhibits a considerably high magneto-resistance effect as compared with magnetic metal alloys. Next to this, studies have been made on a spin-valve structure having, as one unit, a ferromagnetic metal/insulator/ferromagnetic metal system. The spin-valve structure has already been applied to magnetic random access memories, etc. and put into practical use as products. In addition, development of quite new magneto-resistance materials has recently been going on with the aim of establishing materials exhibiting a further higher magneto-resistance effect.
The first condition for enhancing the performance of a device using the magneto-resistance effect is that the materials have a high rate of change in magneto-resistance (magneto-resistance ratio). Here, the magneto-resistance ratio is defined by a ratio of the change ΔR in magneto-resistance resulting from application of a magnetic field, which change is the difference between the maximum resistance value Rmax and the minimum resistance value Rmin, to Rmin, i.e. ΔR/R=100×(Rmax−Rmin)/Rmin (%).
The second important condition is that the materials have high sensitivity to the magnetic field. When the materials are applied to electronic devices, such as a memory device, the devices have to be driven by application of a magnetic field of 100 0e (oersted) that can be electrically generated with ease and that can also be generated within the devices. In order for the devices to be used as magnetic field sensors, such as an automobile speed sensor and a positioning sensor, the devices have to be driven by application of a magnetic field that can realize a magnetic field range that can be generated using a permanent magnet and that can take a distance between an appropriate sensor and the permanent magnet, i.e. not more than 1,000 0e.
Though the high magneto-resistance ratio and high sensitivity of the materials are important characteristic values in developing devices, it is actually indispensable to industrialization using the materials that the materials have good compatibility with the existing semiconductor technologies. For example, materials that cannot be incorporated into a line of semiconductor fabrication using the main materials in the semiconductor technologies, such as silicon and gallium arsenic, or materials requiring great labor for the incorporation are disadvantageous from the standpoint of the industrialization. In most cases, materials containing magnetic metal elements, such as iron, chromium and cobalt, are not suitable for the industrialization. Furthermore, it is greatly demanded from the economical point of view to simplify the device-fabricating steps.
It goes without saying that it is difficult for the devices to be used as actual magneto-resistance effect devices insofar as the characteristics of the devices cannot be manifested at room temperature.
TABLE 1-IMagneto-resistanceRequiredProcess-Room-Features of magneto-resistanceratiomagneticmatchingtemp.Nr.effect device(room temp.)field (Oe)with LSIoperationReference materialaPermalloy2.51,500PossiblePossibleJMMM, Vol. 83, p. 113 (1990)bMagnetic resistance6510,000PossiblePossibleAPL, Vol. 58, p. 2710 (1991)multi-filmcSpin valve film 120<100PossiblePossibleJAP, Vol. 81, p. 3741 (1997)dSpin valve film 210<100PossiblePossibleJP-A 2000-150985eGranular magnetic film201,000PossiblePossibleJP-A 2000-156531fUranium compound50020,000ImpossibleImpossibleJMMM, Vol. 104-107, p. 19 (1992)gPerovskite oxide film 1101070,000ImpossibleImpossibleU.S. Pat. No. 5,665,664hPerovskite oxide film 21070,000ImpossiblePossibleNature, Vol. 57, p. 291 (1990)iIndium antimony30010,000SuitablePossibleAPL, Vol. 57, p. 291 (1990)jSemiconductor201,000SuitablePossibleIEEE, Trans. Magn. Vol. 34,hetero-structurep. 1300 (1998)kMercury compound101,000PossiblePossibleJP-A HEI 11-112057semiconductorlIndium antimony100500PossiblePossibleICPS abstract book part II, p. 342 (2000)mMnSb granular film 13,5005,000PossiblePossibleJP-A HEI 11-204443, JP-A HEI 11-82062USP pendingnMnSb granular film 27,30015,000PossiblePossibleJP-A HEI 11-204443, JP-A HEI 11-82062USP pendingoInvention thin film 145030SuitablePossibleFIG. 5pInvention thin film 22,200500SuitablePossibleFIG. 5qInvention thin film 39,0001,000SuitablePossibleFIG. 5rInvention thin film 4>100,0007,000SuitablePossibleFIG. 5
As is clear from Table 1, the materials exhibiting high magneto-resistance effect, such as materials f, g and h in Table 1, have drawbacks that these can only operate at low temperatures and that these require an extremely high magnetic field. Materials i and j in Table 1 that suitably match a semiconductor device-fabricating process, when operated under a magnetic field of not more than 100 0e, these produce a very small output of electrical signal. Materials c and d in Table 1 that are applied to electronic devices exhibit a low magneto-resistance ratio.
The inventors recently discovered a new magneto-resistance effect. This effect is manifested when the electron avalanche phenomenon occurring in a magneto-resistance material is frozen through application of a magnetic field. The inventors named this phenomenon a magneto-resistance switching phenomenon and disclosed it in detail in Applied Physics Letters, Vol. 76, No. 3 (2000) 357; Applied Physics Letters, Vol. 76, No. 13 (2000) 1743; Applied physics Letters, Vol. 76, No. 18 (2000) 2600; Journal of Applied Magnetism, Vol. 24, No. 4-2 (2000) 451; and Journal of Applied Magnetism, Vol. 24, No. 4-2 (2000) 499.
As described above, the conventional magneto-resistance devices could only operate at low temperatures or required an extremely high magnetic field. In the case of the conventional devices suitable for mass production, a signal was too small to use them under a practical magnetic field of not more than 100 0e. The conventional devices applied to electronic devices had a small magneto-resistance ratio.
In view of the above, the present invention has been accomplished, and its object is to provide a magneto-resistance effect device exhibiting a very high magneto-resistance effect at room temperature and therefore exhibiting high sensitivity to a magnetic field.
Another object of the invention is to provide a magneto-resistance effect device capable of being produced through a simple production process.
Still another object of the invention is to provide a magneto-resistance effect device formed of a magneto-resistance material easy to match a semiconductor-fabricating process.
Yet another object of the invention is to provide a magnetic field sensor using any of the magneto-resistance devices mentioned above, such as a magnetic field sensor device, magnetic memory, magnetic switching device or other such device.